As a next generation switching element capable of implementing a high withstand voltage, a low loss, and a high heat resistance, a semiconductor element using silicon carbide (SiC) is prospected and application to a power semiconductor device such as an inverter is expected.
However, an SiC semiconductor device has a large number of problems to be solved. One of them is deterioration in a withstand voltage characteristic of the semiconductor device which is caused by electric field concentration in a termination portion of the semiconductor device (for example, an end of a Schottky electrode in a Schottky barrier diode or an end of a pn junction in a pn diode or an MOSFET (Metal Oxide Semiconductor Field Effect Transistor)).
A typical example of the termination structure which relieves an electric field generated in the termination portion of the semiconductor device includes a guard ring structure, a JTE (Junction Termination Extension) structure, an FLR (Field Limiting Ring) structure and the like. All of them are impurity diffusion layers formed to surround an element region. In general, the JTE structure is provided in order to reduce a surface electric field and has a structure in which an impurity concentration is stepwise reduced outward from the termination portion of the semiconductor device. On the other hand, the FLR structure is constituted by a plurality of impurity diffusion layers having an equal concentration.
For example, the following Patent Document 1 discloses a termination structure in which a guard ring and JTE are combined with each other. In the termination structure disclosed in the Patent Document 1, the JTE having a lower impurity concentration than in the guard ring is provided on an outside of the guard ring. In the Patent Document 1, moreover, there is proposed the technique for forming the guard ring and the JTE under a recess structure provided on a surface of a semiconductor layer, thereby increasing a distance between bottom ends of the guard ring and the JTE in which electric field concentration is apt to occur and the surface of the semiconductor layer and thus relieving an electric field on the surface of the semiconductor layer still more.